The field of the present invention is magnetic separation of solid and liquid phases. More particularly, it relates to magnetic separation useful in heterogeneous assays such as genetic probe assays and ligand-receptor assays such as immunoassays.
It is well known to assay for antigens, antibodies, polynucleotides and other target substances present in a liquid sample by reactions using a labeled reagent, the assay being affected by measuring the amount of label either bound in a complex of the target and labeled reagent bound to a solid phase or remaining unbound in solution. Various techniques for quantifying labels include, for example, radiometric, enzymatic, fluorometric, and chemiluminescent methods. In all of these procedures, it is generally necessary either to separate the complexes formed from the remainder of the reaction mixture, or to separate the free unbound labeled reactant from the remainder of the reaction mixture in order to measure the amount of label in either part. This separation step is difficult to perform cleanly and is therefor a source of error in the procedures.
Prior to quantification, it is generally necessary to separate the complexed products from the surrounding medium. One such separation technique is the use in immunoassays of magnetically attractable particles which specifically bind either the complexes formed or the unbound labeled reactant and applying a magnetic field to draw and hold the particles and allow the surrounding medium to be flushed away or removed. Such methods and devices are disclosed in U.S. Pat. Nos. 4,141,687, 4,272,510, 3,985,649 and 4,438,068. These patents may be consulted to provide background on immunoassay techniques and magnetic separation procedures.
Although existing methods and apparatus are known for the magnetic separation of solid phase immunoassays, the known procedures have limitations including specific requirements as to magnet size, magnet orientation of both magnetic axis and the north/south orientation, as well as various process constraints and inefficiencies. An improved method and device for performing magnetic separation for heterogeneous immunoassays, genetic probe assays and other assays is desired for repetitive laboratory use.